1. Field of the Invention
The invention generally relates to magnetic sensor methods and systems, and more particularly to probing devices associated with magnetic sensors and spin-dependent tunneling (SDT) sensors.
2. Description of the Related Art
Magnetic films are used in a variety of devices that include magnetic random access memories MRAM and magnetic recording media. In the magnetic recording industry, information is generally stored as magnetic bits on thin ferromagnetic films. In reading such magnetic bits, the magnetic recording industry requires detection devices that measure the magnetization of small regions along a magnetic track. Computer storage devices, such as, for example, magnetic disk drives, utilize read/write heads to store and retrieve data. A write head stores data by utilizing magnetic flux to set the magnetic moment of a particular area on a magnetic media. The state of the magnetic moment is later read by a read head, which senses the magnetic fields.
Presently, quality read heads utilize giant magnetoresistance (GMR) read heads, which are spin valves or similar to spin valves. Such GMR thin-film read heads employ magnetoresistive material, generally formed in a layered structure of ferromagnetic magnetoresistive and non-ferromagnetic non-magnetoresistive materials, to detect the magnetic moments of the data bits on the media. A sensing current is passed through the magnetoresistive material to detect changes in the resistance of the material induced by the data bits as they pass the read head. Spin valves are usually formed as three layer structures including a hard or pinned ferromagnet, a soft ferromagnet, and a thin intervening conductor. Another device for measuring local magnetizations is a magnetic force microscope. Magnetic force microscopes are scanning tunneling microscopes with ferromagnetic tips.
The magnetoresistivity of GMR devices depends on the ease with which electrons can make transitions between the soft and hard ferromagnetic materials. Electrons traveling along the layers without making this transition do not contribute to the magnetoresistance. Thus, the layers in a GMR device must be thin in order for a signal generated by a field change not to be too small. Another type of magnetic sensor is a spin dependent tunneling SDT sensor. An SDT sensor consists of a hard ferromagnetic layer, a soft ferromagnetic layer, and a thin insulating intervening layer. The tunneling impedance between the two ferromagnets is less when the magnetizations of the two ferromagnets are parallel. An example of a GMR sensor is the GMR sensor disclosed in the above-mentioned U.S. patent application Ser. No. 10/434,337. Recent magnetic modeling calculations with a single thin layer, have achieved less than optimum results because if the sense layer is very thin, it will not affect the magnetic field flux lines. The ratio of the field in the sense material when it was over a soft magnetic material to the field to when it was not over the soft magnetic material was found to be approximately only 1.14. This small field change makes it difficult to read magnetic information.
Other conventional methods for measuring local magnetization such as magnetic force microscopes and electron microscopes with magnetic electrodes that analyze the spin direction of tunneling electrons can be cumbersome, inefficient, and expensive.
Therefore, while the above-referenced U.S. patent application discloses embodiments that were satisfactory for the purposes for which they were intended, there remains a need for improved systems and methods for probing the magnetic properties of materials. In particular, a need exists for improved methods and systems for measuring the extent to which a local surface region of a material can be magnetized. Conventional magnetic sensing systems and methods are limited because most other magnetic probes do not measure how easily a material may be magnetized. Furthermore, most other conventional devices do not readily permit varying the length over which the material's magnetic properties are being probed. Thus, there is a need to overcome the limitations of the conventional systems and methods and to effectively probe the magnetic properties of a particular material.